Bollettino valanghe

Continental

Valdez Avalanche Center
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Pericolo valanghe

Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 8 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The avalanche hazard is Moderate at all elevations.  New snow will make human triggered avalanches possible 1-2 feet in depth.  Watch for areas of wind stiffened snow where the sensitivity of the snow will be higher.  Natural avalanches are unlikely.

Public avalanche forecasts are issued Wednesday-Sunday at 8 am.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

      After a long break, snowfall has finally returned to our area.  Storm totals range from 6-10 inches with Valdez receiving 6 " in the last 24 hours, with  .4" of snow water equivalent.  The new snow is rather light and fluffy and is falling on a variety of surfaces, including bare ground, a persistent rain crust (weak layer), knife hard wind slabs, and sastrugi.  The new snow will bond differently to each surface, so expect conditions to change, even within a small area.

    Pay attention to the stiffness (cohesion) of the new snow and use hand pits to determine how well bonded the snow is to the underlying surfaces.  In many areas the snow is light and fluffy and is unlikely to produce slab avalanches at this time.  Areas where the new snow has been redistributed and stiffened by the wind will be the spots where triggering an avalanche will be possible today.  Winds were blowing from the southeast yesterday as snow was falling and have swithched to northeast sometime around midnight.  Northeast winds are expected to be moderate and mostly confined to wind channeled areas such as the Thompson Pass summit.  Changing wind direction means that multiple aspects could be loaded, pay attention to the stiffness of the surface snow and be alert to changes.

    Shooting cracks and collapsing were observed yesterday, especially near valley floors.  A lack of cohesion in the surface snow made slab avalanches unlikely within the new snow.  Watch for these signs of instability in tandem with wind stiffened snow.

    Persistent slab:  Old persistent wind slabs that overlie the faceted (weak) 12/1 rain crust may still be possible to trigger up to 1' in depth in isolated locations below 3500'.  These old wind slabs are now masked by new snow and will be difficult to visually identify.  They exist in terrain that commonly holds wind slabs during North wind events.  

    New snow is loading the 12/1 persistent weak layer below 3500', but once again will require cohesion of the surface snow for slab avalanches to be triggered.

     

Avalanche Discussion

Avalanche activity in the last 72 hours:  None

Forecast Discussion:  

We are at the very beginning of the snowpack loading process, following a prolonged drought and strong winds.  The December wind has created a ton of spatial variability in our snowpack, but a common theme is faceted snow.  At this point the dry and uncohesive snow we have received is not enough to affect deeper layers in the snowpack, and instabilities will be confined to the surface where the wind has stiffened the new snow.

Below 3000-3500' a fragile rain crust with facets underneath exists and has shown signs of instability in the last week where it is buried by wind slab.  Once a cohesive slab exists over this layer, expect for the layer to become reactive to human and machine triggers.  This setup may already exist in isolated locations.  Areas where wind slabs are expected to form today are also areas where this layer is likely destroyed by previous strong winds.  This elevation band, where the rain crust exists is the first area where facets are expected to become reactive once a sufficient load is deposited, potentially this weekend.

Above 3000' the lack of the rain crust allowed the wind to scour much deeper into the snowpack, creating large areas of bare ground and thick knife hard wind slabs that overlie weak faceted snow.  These thick wind slabs will be able to support much larger loads before facets are affected, than the rain crust.  To be clear, I'm not suggesting that avalanches are unlikelly at upper elevations at this point.  But rather that hard slab avalanches that fail beneath the December wind slab are unlikely at this time.  Avalanche activity at upper elevation is expected to be confined to the surface snow with the December wind slab acting as the bed surface.  It is unclear at this point how well new snow will bond to these rock hard wind slabs.  Direct observations will be necessary.

Additional Details:  Be aware that the new snow is masking what was bare ground last week in some areas.  Large expanses of bare ground exist near Thompson Pass in popular terrain such as Moonlight, Loveland, Oddessey, and Catchers Mitt.  Use caution in all terrain above 3000' to avoid hitting rocks.

There is no field data from the Maritime zone due to low snow coverage and thick brush restricting access.  Check out the season summary tab for more information on the development of the snowpack.

 

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